The present invention relates to an image scanning apparatus having a scanning carriage driving system for reading image data. It relates particularly to the image scanning apparatus having a rotating shaft coupling, for example, it is assembled between a stepping motor shaft of a driving side and a shaft of a driven side. It is composed to suppress transmission of a vibration from the motor shaft side to the driven side in the scanning carriage driving system.
The image scanning apparatus is used for example for an electronic filing which stores a lot of various kinds of documents as image data. A image scanner has been used conventionally as the image scanning apparatus. Well known type of image scanners is a flat-bed type in which a document is put on a document table made of glass by hand-setting and an automatic document feeder (ADF) type in which comparatively small sized documents are automatically fed.
Such an image scanning apparatus usually has the scanning carriage driving system for reading image data. As a driving source of the scanning carriage driving system, a stepping motor is frequently used but the vibration and the periphery speed fluctuation of the motor shaft transmit to the carriage. By this reason, while the carriage scans under the document table, the moving speed fluctuates slightly as a result, the scanned image may be unclear or may have a distortion.
One of the means to suppress the transmission of the vibration from the stepping motor to the driven side is to provide a damper on the motor shaft as described in Japanese Patent Application Examined Publication No.H6-67173. The damper is composed of a ring-shaped metal flange around the motor shaft, an elastic body made of rubber that is disposed around the entire outer periphery and an inertia body made of metal unifying into the entire outer periphery of the elastic body. In such a damper, the motor shaft rotates smoothly in a wide range from a low velocity to a high velocity. The elastic body uniformly transmits a rotation force of the motor shaft to the inertia body. Then the inertia body vests a repulsion force against the rotation force of the motor shaft and moreover the inertia body itself suppresses a damped vibration of a transient response characteristic of the motor without being a vibrator.
Thus, the transmission of the vibration to the carriage is suppressed by attaching the damper like above-described on the shaft of the stepping motor. Therefore, the image scanning performance improves comparing with the case of direct coupling between the motor shaft and the driven side.
The damper which was disclosed in the above Examined Publication describing forcibly suppresses the vibration of the motor shaft by operating the elastic body and inertia body, and also damps the vibration for the motor side which acts as the vibrating source, thus enables to reduce the effect on the driven side.
However, the vibration of the motor is due to a rotation of a rotor which is generally heavier than a motor shaft. The vibration of the motor can not be completely suppressed even if the vibration of the motor shaft is suppressed to some degree. Then the motor shaft is directly coupled to the driven side through a coupling or connected to the driven side through a gear train or a belt for speed reduction, any factor to damp the vibration is not included between the motor shaft and the driven side. Therefore, a residual component of the vibration of the motor which was unable to suppress by the damper is transmitted to the driven side through the motor shaft.
Thus, the construction in which the motor shaft is connected to the driven side by providing the damper around the motor shaft, it is impossible to sufficiently suppress the transmission of the vibration to the driven side. Due to this, there was a limitation in improving the scanning accuracy of the image even if such a damper is assembled in the carriage driving system whose main focus is uniformity and stability of the scanning speed.
The present invention aims to offer the image scanning apparatus with a good image scanning is possible by effectively suppressing the transmission of the vibration from the motor side to the driven side and assembling the rotating shaft coupling which can make the action of the driven side stable in the carriage driving system.
An image scanning apparatus of the present invention comprises:
(a) a document table for putting a document on;
(b) a carriage having a scanning module for reading an image data of the document by scanning the document;
(c) a driving mechanism for driving the carriage; and
(d) a rotating shaft coupling assembled in the driving mechanism;
wherein the rotating shaft coupling has a plurality of rotating-shaft-coupling-members, one of the rotating-shaft-coupling-members being multi-layered by a coupler connecting a shaft thereto, an elastic body and an inertia body which has a mass activating a torsion load in a rotating direction when the elastic body is rotating, and a plurality of the rotating-shaft-coupling-members are assembled into the rotating shaft coupling.
According to this construction, even if the driving motor of the driving mechanism is a stepping motor, the vibration from the motor side is not transmitted to the driven side and moreover a smooth rotation at the driven side can be obtained and the mechanical parts of the driven side can be functioned with a high accuracy.